1. Field of the Invention
This invention relates to plastic bags, and more particularly to a pack of T-shirt bags, merchandise bags, trash bags, and the like made preferably of polyolefins, and method of manufacturing same, which can be used with or without bagging racks and which provide for self-opening of the bags as each bag is removed from the pack of bags.
2. Description of the Prior Art
Since the mid-1980's, the use of plastic shopping bags has grown dramatically due to the great advantage plastic bags have over bags made of other materials, such as paper. Many types of plastic bags are made of low or high density polyethylene (LDPE and HDPE, respectively), but can be made of any of the polyolefins. LDPE and HDPE bags are stronger, lighter and much more compact to store than paper bags, saving valuable storage space at the merchants' checkout counter and storage areas. These attributes also make these bags less expensive to transport. LDPE and HDPE bags can be manufactured and sold at a fraction of the cost of competing paper bags, making them the bags of choice for merchants. LDPE and HDPE bags are also actually more environmentally friendly than paper bags since they require about 70 percent less energy to manufacture than competing paper bags and are readily recyclable, and when not recycled, are non-toxic when incinerated or disposed of in landfills.
Many groceries stores and other merchants now use a style of plastic bag to bag groceries and other merchandise commonly referred to as T-shirt bags. T-shirt bags are pleated bags which are closed, by heat sealing, at a bottom edge, and have a pair of integral loop handles extending upwardly to define an open mouth of the bag therebetween. Because high density polyethylene (HDPE) has a greater resistance to stretching and deformation than LDPE plastic, HDPE plastic is generally used for making T-shirt bags, although LDPE and other polyolefins can also be used. T-shirt bags are normally provided in packs of aligned bags and these packs of bags are usually used in conjunction with bagging racks.
T-shirt bags are generally manufactured by the following process. A continuous tube of HDPE plastic, or other plastic materials having the desired color, thickness, and diameter is formed on a extrusion machine. The continuous plastic tube is then passed over rollers to roll the continuous plastic tube onto a spool. If the bags to be formed from the continuous tube of HDPE are to be printed on one or both sides, the newly formed continuous plastic tube will be subjected to corona surface treatment, wherein the side or sides of the continuous flattened tube of plastic to be later printed will be passed by a high voltage corona discharge electrode. Corona surface treatment affects electrical and chemical changes on the plastic's outer surface to prepare that surface of the bag for printing. Regardless of whether or not the bags will be printed on one or both sides, it is a common practice in the plastic bag manufacturing industry to corona surface treat the entire outer surface of the rolls of continuous plastic tubing so that printing can be done on either one or both sides, if desired. It has been found that corona surface treatment, or other known methods to electrically and chemically change the entire outer surface of the continuous plastic tube, contributes somewhat to the self-opening feature of applicants' plastic bag pack system.
After being corona surface treated and rolled (if the bags might be printed), the roll of continuous plastic tube is unrolled and is then pleating on a pleating machine. Following this, a bagging machine heat seams and cuts sections of the pleated tube at top and bottom edges to form closed and flattened pleated bags of a desired length and width, with the pleated sides being at both sides of the flattened pleated bags. These sections are often referred to as pillowcases. Further downstream of the heat seaming and cutting step, the pillowcases are stacked in aligned stacks. Thereafter, hydraulic die cutting or other cutting methods are utilized to remove material at the stacked pillowcases' top portions to form the handles with apertures passing therethrough, and to form a mouth tab portion with an aperture to support the pack of self-opening bags on hooks positioned on a bagging rack. Each loop handle will comprise four layers of plastic material since they are cut out from the pleated side portions of the bag.
Despite the many advantages HDPE T-shirt bags have over paper bags, they are not self-standing like thicker and stiffer paper bags with a discreet flat bottom. This is due to their relatively thin and flexible material. In grocery stores settings, where quick and easy loading of bags is desirable, packs of T-shirt bags are generally supported on a bagging rack as merchandise is loaded into the bags to overcome the lack a of self-standing ability.
There are several popular styles of T-shirt bags available in packs of bags and bagging racks for use therewith, two main types of which will be discussed.
In one type of pack of T-shirt bags and bagging racks used therewith, the bagging rack has a support base, a wire rear wall with a tab receiving hook, and two wire arms extending forwardly over the base. In the center top portion of the arms, the wire is formed so as to have a section which will spread and hold apart the handles of T-shirt bags engaged therewith to open up the mouth of the T-shirt bag. The pack of T-shirt bags used with these styles of bagging racks consists of a stack of overlapped and aligned bags which have a lower bag portion with two handles extending upwardly at both sides of the mouth of the bags. A central tab portion is provided on the mouth of the bags between the two handles, and the central tab portions of the pack of bags are heat-sealed together. The heat sealed central tabs thus form a stack or book of central tabs and have a central tab slit formed therethrough. The central tab slit is engaged with the tab receiving hook on the rear wall of the bagging rack, and the book of central tabs will remain engaged therewith, even after individual bags are removed. Below the central tab slit a tearing slit is provided which traverses almost the entire distance of the central tabs except for a small distance at both sides of the central tab portion. The tearing slit allows the individual bags to be torn off the pack of bags as they are needed, and looped onto the bagging rack.
A second major type of pack of T-shirt bag, and bagging rack designed to be used therewith, are disclosed in U.S. Pat. No. RE 33,264 to Baxley et al. Another version of this style of bagging rack is disclosed in U.S. Pat. No. 4,840,336 to Stroh et al. Both of these bagging racks have a bottom support base and a rear wire wall with a tab receiving hook located thereon. However, to open up each individual bag for loading, instead of looping the handles of the bags over the top of the support arm one at a time, as is done with the first type of pack of bags and rack, these racks have two handle support rods extending forwardly from the rear wire wall of the racks. The pack of T-shirt bags used with these styles of racks are similar to those used with the first type of rack, except that aligned apertures with flaps are formed on each handle of the pack of bags, through which pass the handle support rods of the bagging racks.
The prior art packs of T-shirt bags suffer from drawbacks. Prominent among these drawbacks include the lack of a convenient and easy to manufacture self-opening feature, to eliminate the need for the box person to struggle to open up each bag in the pack of bags.
In order to prepare a T-shirt bag for loading with merchandise, only the first layer of the bag material of the top bag, and no other layers must be pulled forward, thereby opening just the top bag. Since the HDPE material is very thin, typically between 1 to 0.5 mil thick (0.001 and 0.0005 inches), it is sometimes difficult for the checkout clerk or box person to grasp just the top layer of bag material. One can often see a sponge or source of tacky material, such as a glue stick, retained at the top of bagging racks, with which the checkout clerk or box person can dampen his or her fingers to aid in grasping just the top layer of material of the bag. However, this takes additional time and effort in the bagging process. This cycle will have to be repeated with each successive bag to be loaded.
In addition, the prior art bag packs systems all leave waste books of heat bonded central tabs on the bagging rack. These books accumulate on the bagging rack and must be thrown out. Thirdly, in those styles of packs of bags which employ a central tab slit through their central tabs for mounting the pack of bags on a tab receiving hook of a bagging rack, it is sometimes difficult to engage the slitted central tab with the tab receiving hook. For those styles of bags packs having bagging rack suspension arm apertures defined by flaps through their handles for suspending the bag handles on bagging racks with suspension arms, the presence of the flaps in the apertures often make it difficult for the person loading a pack of bags to place the pack of bags on the rack.
Several approaches have been taken to overcome the lack of a self-opening feature problem. U.S. Pat. No. RE 33,264 to Baxley et al. discloses a pack of T-shirt bags wherein spots of adhesive are placed between the rear walls of the forwardly lying bags and the front walls of the rearwardly lying bags. The use of these spots of adhesive is intended to provide for self-opening of the bags as each successive bag is pulled off the pack of bags on the bagging rack. However, the use of spots of adhesive is undesirable from a cost and reliability standpoint because an extra manufacturing step of depositing spots of adhesive on the growing stack of pillowcases as each subsequent pillowcases is stacked thereon is required.
U.S. Pat. No. 5,074,674 to Kuklies et al. discloses a packs of bags similar to that of Baxley, et al. wherein the front wall of each bag is either relieved or removed in the region of the central tab so as not to be retained by the tab receiving hook on the bagging rack, purportedly allowing the front wall of the bag to be grasped more easily to open the bag. However, this style also requires an extra, and difficult manufacturing step of removing or relieving a portion of only the front wall of each bag. The pack of bags of Kuklies, et al. does not provide for self-opening of the bags.
U.S. Pat. No. 4,877,473 to Snowden et al. discloses a pack of bags wherein the tearing line has a central arched portion which forms a sub tab. This sub tab can be easily grasped and pulled forward to pull the front wall of each bag to open that particular bag. However, each subsequent bag in the pack of bags must be opened in the same manner, and thus the desired self-opening feature is absent.
U.S. Pat. No. 5,087,234 to Prader et al. discloses an easy-open bag pack wherein the easy-open feature results from corona discharge treating a tube of polyethylene film, transverse sealing to form pillowcases of the plastic material, stacking the pillowcases, and applying sufficient pressure to a cutting device to form the handles therein.
U.S. Pat. No. 5,183,158 to Boyd et al. discloses a bag pack and dispensing system wherein the pack of bags has a self-opening feature, which arises out of frangible pressure bonding areas located on the handles, distant the bag rack handle suspension slits, and both below the optional mouth tab and near the lower portions of the pack of bags, near its bottom edge. For a bag pack of the form of Boyd et al., without a suspension mouth tab, the reliability of the self-opening feature as each sucessive bag is pulled off the pack of bags may be compromised. For the bag packs of Boyd et al. with a suspension mouth tab, Boyd et al. teaches the preference of having its mouth tab's front side unattached to the back wall of the mouth tab. Front side free mouth tab structures are more difficult and costly to manufacture than conventional bag structure.
Despite the attempts to overcome the problems associated with these presently available bags, there remains a need for an improved pack of T-shirt bags which (1) can be easily manufactured, yet which provides for reliable self-opening of each bag of the pack of bags, (2) does not leave a book of plastic tabs on the bagging rack, and (3) can be easily placed on a bagging rack.